This invention relates to some improvements in a forced ventilation system for those electric instruments which have electric circuit means that need ventilation, such as semiconductor devices on printed circuit boards, or to such an electric instrument incorporating the improved forced ventilation system.
Electric instruments with a generally boxlike casing have been known and used extensively which have an exhaust fan mounted outside the casing. The air heated by the electronic devices within the casing is drawn by the fan and forced out of the casing in order to keep the devices at operable temperatures.
Being required to be least conspicuous, the fan has usually been mounted on the back of the casing. This fan location has brought about some inconveniences. First, in cases where a multiplicity of terminals are to be arranged on the back of the casing, the fan with its relatively large space requirement has imposed limits upon the latitude of terminal arrangement. Another pronounced inconvenience has been the noise produced by the more or less exposed fan.
There are additional considerations that must enter into the design of a well-ventilated electric instrument, particularly its casing. There must be an optimum airflow through the interior of the casing for most efficient cooling of the components housed therein. The constituent parts of the casing, well designed to assure such airflow, must, moreover, not add substantially to the manufacturing costs of the instrument and must lend themselves to ready assemblage.
The present invention has it as an object to provide a well ventilated electric instrument having a cooling fan incorporated therein so as not to interfere in any way with a desired arrangement of terminals or the like on its casing.
Another object of the invention is to reduce noise production by the fan to a minimum.
Still another object of the invention is to assure optimum airflow through the interior of the casing for most efficient cooling of the components housed therein.
A further object of the invention is to facilitate the manufacture and assemblage of the instrument that accomplishes all the foregoing objects.
Stated briefly, the present invention concerns a ventilated electric instrument comprising a casing having formed therein an air intake port and an exhaust port. A fan is mounted interiorly of the casing for causing airflow therethrough from the intake port to the exhaust port. Electronic circuit means are mounted interiorly of the casing and positioned to be cooled by the airflow, and terminal means are mounted exteriorly of the casing and electrically connected to the electronic circuit means.
Thus, with the fan mounted inside the casing, and preferably away from the back of the casing, terminals or the like can be arranged over a greater area on the casing back, in an ideal pattern or in a greater number than if the fan were mounted to the casing back. Noise production by the fan is also reduced to a minimum.
According to another feature of the invention, the casing has its interior partitioned into an air intake passageway extending along one side of the casing, an exhaust passageway extending along the other side of the casing, and a circuit chamber between the intake and the exhaust passageways. The electric circuit means are mounted in the circuit chamber.
Preferably, both air passageways are open rearwardly of the casing to the atmosphere and closed at their front ends, besides being open to the circuit chamber via inflow and outflow openings in the partitions. These openings in the partitions may be situated closer to the closed front ends, than to the open ends, of the air passageways.
Lying in the circuit chamber, the fan is mounted to the partition bounding the intake passageway in one embodiment of the invention, and to the other partition bounding the exhaust passageway in another. Either way, ambient air is drawn into the circuit chamber via the intake passageway on one side of the casing and exhausted therefrom via the exhaust passageway on the other side of the casing.
The electric circuit means will be cooled most efficiently by being positioned in the flow path of the air through the circuit chamber. The casing itself will also be cooled efficiently as the air streams into the circuit chamber not directly but via the elongate intake passageway and flows out not directly but via the elongate exhaust passageway.
No less significant advantage accruing from the provision of the intake and exhaust passageways is that the circuit chamber is completely closed except for the openings in the partitions. The fan will therefore present little or no noise problem.
According to a further feature of the invention, the casing is constituted of two parts which are designed for ease of fabrication and assemblage and which, moreover, are well calculated to realize all the foregoing features and advantages of the invention. The two parts of the casing are a casing bottom part substantially in the shape of an open-top box, and a casing top part substantially in the shape of an inverted U as seen in the depth direction of the casing. Both casing parts are manufacturable by bending required parts of sheet-metal punchings, and assemblable by interengaging them and fastening them with a minimal number of screws or the like.
The above and other objects, features and advantages of the invention and the manner of realizing them will become more apparent, and the invention itself will best be understood, from the following description taken together with the attached drawings showing the preferred embodiments of the invention.